[The effect of monosodium L-glutamate (MSG) treatment during neonatal period on the pineal function in young female rats].

The purpose of this study is to examine whether monosodium L-glutamate (MSG) influences the function of pinealocytes in female rats. MSG was administered at a does of 4 mg/g body weight to rat pups on days 1 and 3 postnatally. As the rats matured, sexual receptivity as well as proceptivity were observed by testing the lordosis quotient (LQ), rejection quotient (RQ) and solicitation. Pineal function was estimated by measuring the serum level of melatonin and the activity of protein kinase A (PKA) in the pineal gland. Blood samples were withdrawn at light and dark phases for four consecutive days, respectively. The serum concentration of melatonin was determined by radioimmunoassay and the data of each phase were pooled together. The results showed that both the receptivity and proceptivity of MSG-treated female rats were significantly lower than that of the control ones. Melatonin levels during the dark phase were significantly higher than those during the light phase in both control and MSG-treated groups, but whenever in the light or dark phase, the levels of melatonin were the same in both groups. There was no significant difference in PKA activity in the pineal gland between the control and MSG-treated group. These results indicate that MSG used as a neurotoxin to induce hypogonadal status affected neither the PKA activity of pineal gland nor the serum level of melatonin in young female rats. Thus, the decrease in receptivity and proceptivity of MSG-treated female rats was not caused by the alteration of pineal function.